The invention relates to a high-density electronic interconnecting system wherein the physical characteristics of a supporting substrate are chosen according to predetermined electrical properties designed for the system. More particularly, the invention relates to flexible electrical interconnects based on substrates of selected physical properties.
Developments in miniaturization and microelectronics are resulting in electronic components having to rapidly interact and communicate with and respond to each other across microscopic electrical domains. Ball grid array (BGA) technology provides a high density of interconnections per unit area, but mismatches of coefficients of thermal expansion (CTEs) occur when ceramic, silicon, or polymer BGA substrates and printed circuit boards are joined and often result in cracked joints, especially as the size of the substrates and temperature ranges are increased. Besides, the interconnects cannot be designed to a pitch (i.e. the closest separation between two adjacent interconnects) of less than about 50 microns. At very fine pitch, from practical considerations, the interconnect cannot pass through the core of the substrate.
Accordingly, there is a need for innovative packaging techniques capable of providing a high density system of interconnects wherein the interconnects are positioned atop or across the surfaces of a substrate without penetrating the substrate. It is also desirable that the interconnects be provided in close proximity of each other to provide a pitch of about 50 microns or less. It is also desirable that the physical characteristics of the substrates are selected according to predetermined electrical requirements of capacitance, dielectric constant and impedance, among other criteria. It is also desirable for the substrates to be configured to be coupled to each other so as to provide minimal or no clearance between adjoining substrates thereby providing a high-density packaging system of flexible interconnects.